Two methods of estimating the mass of a vehicle are known in the art: a method using a straight direction model algorithm, and a method using both a straight direction model algorithm and a lateral direction model algorithm.
The method using only a straight direction model algorithm includes a method of estimating the mass when there is information on a road surface gradient, and a method of estimating the mass when there is no information on the road surface gradient. When there is information on the road surface gradient, the method supplies information such as traction of the vehicle, inclination acceleration, inclination speed, the road surface gradient, and the like, while the vehicle travels straight, to a recursive least square (RLS) method. When there is no information on the road surface gradient, the method supplies information such as engine torque, brake torque, aero drag torque, engine speed, a rotational resistance constant, and the like, while the vehicle travels straight, to the RLS method. The method using the straight direction model algorithm is simple. However, the method has disadvantages in that the mass of the vehicle can only be estimated when the vehicle travels straight, and some of the variables used are difficult to measure.
The method using both a straight direction model algorithm and a lateral direction model algorithm uses a tire model and calculates the tire force in the straight and lateral directions. Compared to the method using only the straight direction model algorithm, the method using both the straight direction model algorithm and the lateral direction model algorithm can more flexibly estimate the mass of a moving vehicle. However, this method is more complicated, and is susceptible to errors of the tire force due to the tire model.